1. Field
The following description relates to an actuator, and more particularly, to an ElectroActive Polymer (EAP) actuator and a method of manufacturing the same.
2. Description of the Related Art
The term Electroactive Polymers (EAPs) generally refers to polymers whose shape is modified by electric stimulation. However, in a broad sense, EAP may refer to polymers whose shape is modified by chemical stimulation or thermal stimulation, in addition to electric stimulation. EAPs may be divided into types, such as Ionic Polymer Metal Composite (IPMC), dielectric elastomer, conducting polymer, polymer gel, Polyvinylidene Fluoride resins, carbon nanotubes, shape memory polymers, etc.
An EAP is widely used as a material for an actuator, which is a power transfer device to convert electric energy to mechanical energy. For example, an EAP actuator is used in various application devices, such as fluidic lenses, micro cameras, polymer Micro Electro Mechanical Systems (MEMS), bio systems, energy harvesting, etc. In addition, an EAP actuator is used in applications, such as sensors, capacitors, diaphragms, etc.
An EAP actuator deforms up to 5%, as compared with a ceramic piezoelectric actuator having a maximum strain of 0.2%. Accordingly, even a small sized EAP actuator can provide a relatively large displacement. In this regard, EAP actuators have gained a large amount of interest in various fields. For example, the field of varifocal fluidic lenses which are included in a high performance image pickup device in small sized and thin mobile electronic devices. Varifocal fluidic lenses are used to implement various functions, such as an Auto-Focus (AF) function, a zoom function, an Optical Image Stabilization (OIS) function, etc.
An EAP actuator deforms by a fraction of a percent at an electric field about 20 V/μm to 150 V/μm. Accordingly, in order to obtain a great displacement, for example, about 3% to 7%, in an EAP actuator using polymers having a thickness of about 10 μm, the driving voltage needs to be about 200V to 1500V. However, a conventional EAP actuator using such a high driving voltage has limited applications in certain devices, such as mobile electronic devices, which operate on a relatively low driving voltage of, for example 24V or less.
In order to reduce the driving voltage of an EAP actuator, the applicant of the present invention has filed “Electroactive Polymer Actuator and Method for Manufacturing the Same,” Korea Patent Publication No. 2008-0100757, which discloses a multilayered EAP actuator.
The multilayered EAP polymer actuator has a structure in which a plurality of thin polymer layers are laminated on top of each other while alternately interposing driving electrodes that have different electric potentials therebetween. That is, the multilayered EAP actuator has a plurality of unit layers including a polymer layer formed of electroactive polymer and an active electrode formed on the polymer layer. However, if the active electrode is formed using a metal having a high rigidity, the flexural modulus of the multilayered EAP actuator, which has a plurality of active electrodes, is substantially increased and the displacement of the EAP actuator is reduced. In order to minimize the reduction in the displacement of an EAP actuator, the active electrode needs to be formed in a small thickness of several tens of nanometers. Alternatively, in order to minimize the reduction in the displacement of an EAP actuator, the active electrode may be formed using a conductive polymer instead of metal.
Of relevance to the present exemplary embodiments is that Korea Patent Publication No. 2008-0100757 discloses only the lamination of the respective layers therein. However, the present inventors have found that it is desirable to form a multilayer structure such as that disclosed in Korea Patent Publication No. 2008-0100757 using solution casting methods. The reason is that as opposed to film lamination, solution casting does not require transferring and aligning a thin film. Thus, solution casting simplifies manufacture and reduces manufacturing cost of the resulting multilayer structure. Further, solution casting produces a polymer thin film having a desired flat upper surface regardless of the profile of a base structure, and provides a superior adhesive force between layers, and produces a thin film having reduced contamination or defects. In addition, solution casting is desirable because it can be performed in a smaller space than lamination because it requires smaller process steps and equipment.
However, the present inventors found that if the multilayer EAP structure of Korea Patent Publication No. 2008-0100757 is produced by solution casting, the solution casting results in solvent from successive layers penetrating into already-deposited layers, and thus cracking the active electrode, damaging a surface of the EAP layer, or producing an uneven thickness in the thin film. The present inventors thus arrived at a solution as described herein which does not have the above undesirable features.